With the continuous progress of radio technology, a wide range of radio services emerge massively, but the spectrum resources on which the radio services rely are limited, and facing to the increasing user demand for bandwidth, there are situations that spectrum resources are very short; in the traditional fixed spectrum allocation mode, on the other hand, the utilization of spectrum resources is not high. In a sense, this spectrum allocation system in which the spectrum resources are fixedly allocated to the authorized systems results in extreme shortage of the spectrum resources. The cognitive radio (CR) technology breaks the fixed spectrum allocation system in the traditional sense, and dynamically allocates the spectrums between systems, improving the efficiency of spectrum utilization. Studies found that the spectrum resources of the broadcast television system have room of availability to a large extent, for example, some radio spectrums of the broadcast television system have not been used in some areas; although some spectrums of the broadcast television system have covered some areas, but are not used in some moments, the overall utilization is relatively low. The fixed spectrum allocation mode makes the abovementioned unused spectrum resources unable to be reused, for example, the resources cannot be used by the International Mobile Telecom (IMT) system. The cognitive radio technology solves this problem, that is, the IMT system opportunistically occupies the unused TV White Space (TVWS) in space and time of the broadcast and TV system by obtaining information of the broadcast and television system with the cognitive radio technology, thereby improving the spectrum (authorized spectrum) utilization of the broadcast and television system and releasing the shortage of spectrums in the IMT system.
The cognitive radio system can “opportunistically” use the channels (namely the TVWS) which the primary user (television broadcasting system) does not use at specific times and locations. Therefore, the TVWS spectrums which the cognitive radio system can use are constantly changing, for example, due to the arrival of the primary user (that is, the primary user re-occupies the TVWS) or other reasons, the cognitive radio system must exit from the TVWS spectrum currently in use, or is re-allocated with other TVWS spectrums (that is, exit from the TVWS spectrums currently in use, and be reconfigured with other TVWS spectrums), and the reconfiguration delay may also cause interruptions in the user equipment (UE) service.
The handover technology is one of the key technologies of the mobile communication system, a good handover algorithm can provide the user who has a handover calling request with more efficient and reliable handover service between two adjacent base stations, thereby providing system communication quality and system capacity. The serving cell of the user equipment before the handover is called a source cell, the base station to which the source cell belongs is called a source base station; the cell to which the user equipment prepares to hand over (i.e. the cell that becomes the serving cell of the user equipment after a successful handover) is called a target cell, and the base station to which the target cell belongs is the target base station.
Typically, the handover determination technology applied in the communication system (such as the LTE) is mainly that: the UE measures the signal strength and signal quality of the source cell and adjacent cells, and reports the measurement result to the base station to which the source cell belongs; the base station to which the source cell belongs judges whether to trigger a handover or not in accordance with the preset threshold, and selects a target cell based on the measurement result of the UE; the case that the target cell is a cell (such as a cell using the TVWS spectrums) in the cognitive radio system is not considered in the handover process in the related art. When the target cell is a cell in the cognitive radio system (such as a cell using the TVWS spectrums or spectrums authorized to other systems), and there will be the following problems if the handover determination method in the related art is still used:
1. in a UE handover process, a spectrum resource reconfiguration occurs in the target cell, for example, reconfigured from the TVWS spectrum f1 to f2, at this point, if the UE does not know that the spectrum resources of the target cell are changed, the UE cannot find the target cell determined previously, resulting in a handover failure, and even if the UE is informed of the change of spectrum resources in the target cell, the frequency point f1 measurement result of the target cell and the handover decision are also invalid due to the change of the frequency point, that is, the f2 may not be suitable for the UE handover, which may also cause a handover failure;
2. shortly after the UE hands over to the target cell, a spectrum resource reconfiguration occurs in the target cell, the UE also will be reconfigured, and the UE's service will be affected by the reconfiguration delay, if the reconfiguration time of the target cell is too long, it may result in interruptions in the UE's service;
3. when the base station to which the source cell belongs selects a target cell, it does not consider the spectrum properties of the target cell, specifically, whether the target cell is a cell using the TVWS spectrums or the spectrums authorized to other radio access technology cell communication systems or not is not taken into account, but by default the target cell uses the authorized spectrums; since the TVWS spectrum cell may have spectrum resource reconfigurations, it will lead to an increase in the number of UE handovers.